The present invention relates to a control apparatus for a multiple unit air conditioning system, and particularly to a control apparatus which first adjusts the pressure of refrigerant in a compressor in order to prevent the compressor from being subjected to high pressure and then rapidly initiates the next system operation by turning off the compressor after a predetermined delay interval from the time that the independent indoor devices are turned off.
Conventionally, an indoor air conditioning refrigerant cycle is designed as shown in FIG. 1. An indoor device 1 is installed in a room of a building and is composed of an evaporator 3, an expansion valve 2 and a solenoid valve 4. The evaporator 3 cools the air in the room by heat-exchanging the air by changing low temperature and low pressure liquid refrigerant into gas. The expansion valve 2 changes the liquid refrigerant which is high in temperature and high in pressure into liquid refrigerant which is low in temperature and low in pressure. The solenoid valve 4 opens or closes to control the flow of the liquid refrigerant that is sent to the indoor device 1 according to the control signal from a refrigerant control section. Refrigerant distributor 5 distributes liquid refrigerant to the evaporators 3. Compressor 6 receives low temperature and low pressure gas refrigerant from the evaporators 3 and compresses the gas refrigerant thereby heat-exchanging the heat produced by compressing the air around it which changes the gas refrigerant into a gas refrigerant with a high temperature and high pressure. Pressure relief valve 8 at the outdoor device diverts the refrigerant from the inlet of the compressor 6 to a condenser 7 when the pressure of the refrigerant is higher than a predetermined pressure. Bypass conduit 9 diverts the refrigerant to a high pressure refrigerant distributor 5 thereby balancing the pressure.
In the multiple unit air conditioning system which is designed as described above, if all evaporators 3 in the indoor devices 1 are turned off, the compressor 6 is also simultaneously turned off. Accordingly, when all evaporators 3 in the indoor devices 1 are turned off, as shown in FIG. 1, the solenoid valves 4 of indoor devices 1 the refrigerant, so that the refrigerant in the outdoor device does not flow into the indoor devices 1. At this time, the refrigerant discharged from the compressor 6 reverses direction which causes the compressor 6 to become over-pressured. Because of the unbalanced pressure generated in the compressor 6, the compressor 6 becomes overloaded and the rotation shaft of the compressor 6 may cause the shaft to become unbalanced and disposed at an abnormal position where the compressor does not operate efficiently. In a conventional apparatus, in order to solve this problem, the pressure balance is achieved by the bypass conduit 9 until the rotation shaft of the compressor 6 returns to the normal position. However, because the pressure balance cannot be achieved without the passage of some time, the conventional apparatus has the problem that it does not restart rapidly.
A typical example of the prior art is disclosed in Japanese Utility Model Laid-Open Sho 62-12446. This apparatus can change, at any time, the number of the connected units to a different arbitrarily determined number of units. However, it does not prevent the compressor from being overloaded when all units in the indoor device are turned off.